Punching process with magnetostrictive power source

ABSTRACT

A method and assembly for punching a hole in material provided. A magnetostrictive device  14  includes a coil  26,  a magnetostrictive member  22,  and a punch  28  operatively associated with the magnetostrictive member  22.  The magnetostrictive member  22  is constructed and arranged to lengthen, when exposed to a magnetic field created by the coil  26,  thereby moving the punch  28.  Material  12  to be punched is associated with the punch  28.  The coil is energized to create a magnetic field and thus lengthen the magnetostrictive member  22  so that the punch  28  moves through the material  12,  creating a hole in the material  12.

This application is claims the benefit of U.S. Provisional ApplicationNo. 60/581,275, filed on Jun. 18, 2004, which is hereby incorporated byreference in its entirety.

FIELD OF THE INVENTION

This invention relates to punching small orifice holes and, moreparticularly, to the use of a magnetostrictive device as the drivingforce for punching orifice holes into an orifice disc that is used forfuel injectors.

BACKGROUND OF THE INVENTION

Conventional devices for supplying the force to punch orifice holes inan orifice disc used for a fuel injector include mechanical presses, aircylinders, air/oil cylinders, hydraulic cylinders, and electromagneticsolenoids. Except for the electromagnetic solenoid, these devicesdeliver the driving force at a relatively slow velocity. Thedisadvantage of using an electromagnetic solenoid is that it isphysically large and not compact as is necessary for driving individualpunches.

Thus, there is a need to provide a cost-effective, high-velocity andcompact device as the driving force for moving an individual punch inmaking holes, such as orifice holes in an orifice disc.

SUMMARY OF THE INVENTION

An object of the invention is to fulfill the need referred to above. Inaccordance with the principles of the present invention, this objectiveis achieved by a method for punching a hole in material. Amagnetostrictive device is provided and includes a coil, amagnetostrictive member, and a punch operatively associated with themagnetostrictive member. The magnetostrictive member is constructed andarranged to lengthen, when exposed to a magnetic field created by thecoil, thereby moving the punch. Material to be punched is associatedwith the punch. The coil is energized to create a magnetic field andthus lengthen the magnetostrictive member so that the punch movesthrough the material, creating a hole in the material.

In accordance with another aspect of the invention, a punch assemblyincludes a die constructed and arranged to support material to bepunched. A magnetostrictive device includes a coil, a magnetostrictivemember, and a punch operatively associated with the magnetostrictivemember. The magnetostrictive member is constructed and arranged tolengthen when exposed to a magnetic field created by the coil. When thecoil is energized and the magnetostrictive member lengthens, the punchmoves through the material and into the die, thereby creating a hole inthe material.

Other objects, features and characteristics of the present invention, aswell as the methods of operation and the functions of the relatedelements of the structure, the combination of parts and economics ofmanufacture will become more apparent upon consideration of thefollowing detailed description and appended claims with reference to theaccompanying drawings, all of which form a part of this specification.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be better understood from the following detaileddescription of the preferred embodiments thereof, taken in conjunctionwith the accompanying drawings, wherein like reference numerals refer tolike parts, in which:

FIG. 1 is a schematic illustration of punch assembly including amagnetostrictive device as a driving force for a punch to punch a holein material in accordance with the principles of the present invention.

FIG. 2 is a schematic illustration of punch assembly according toanother embodiment of the invention, including a mechanical amplifier.

DETAILED DESCRIPTION OF THE EXEMPLARY EMBODIMENT

With reference to FIG. 1, a punch assembly, generally indicated at 10,is shown for punching small holes in material 12. The punch assembly 10includes a magnetostrictive device, generally indicated at 14, of thetype for example, as disclosed in U.S. Pat. No. 6,570,474 B2, thecontents of which is hereby incorporated by reference in its entiretyinto this specification. In the embodiment, the magnetostrictive device14 includes a steel cylindrical housing 16. A threaded magnetic steelend cap 18 at the distal end of the cylindrical housing 16 supports asoft steel shim 20. A magnetostrictive member 22, preferably ofTerfenol-D, is coaxially positioned within both the housing 16 and acylindrical polymer bobbin 24, such that the distal end of themagnetostrictive member 22 is in contact with the soft steel shim 20. Acoil 26 is provided about the bobbin 24, the function of which will beexplained below.

The assembly 10 includes a hardened magnetic steel piston 28, defining apunch, moveably positioned at the proximal end of the magnetostrictivemember 22 within a bore 29 of a conventional punch holder/stripper plate30. A return spring 32 urges the piston 28 into contact with theproximal end of the magnetostrictive member 22, thereby exerting apreload on the magnetostrictive member 22. The spring 32 is providedbetween a surface of the piston 28 and a surface of the punchholder/stripper plate 30. According to a presently preferred embodiment,the magnetostrictive member 22 should be prestressed to a nominal value(i.e., about 7.6 MPa for Terfenol-D) to maximize magnetostriction. Thisprestress is preferably provided by a high spring rate disc spring 32(e.g., chrome-vanadium steel belleville springs) chosen and stressed tooptimize their cycle life.

In operation, the steel piston 28 moves downwardly under a force exertedby the magnetostrictive member 22 due to the magnetostrictive member 22lengthening as a result of being exposed to a magnetic field created byenergizing the coil 26. Thus, the end 34 of the piston 28 punches a holethrough the material 12 that is supported by a die 36. After punchingthe hole in the material 12, the end 34 of the piston 28 is received ina bore 38 in the die 36. The punch holder/stripper plate 30 guides thepunch and also holds the material 12 down as the punch 28 is pulled out.The bore 38 and the end 34 of the piston 28 are preferably round tocreate circular holes, but they can be of any configuration to producethe desired shaped hole in the material 12. When current is removed fromthe coil 26, the magnetostrictive member 22 returns to its original,unstretched length. The lengthening and contraction of themagnetostrictive member 22 can occur in milliseconds.

The punch assembly 10 is particularly useful in the manufacture oforifice discs (e.g. material 12 in FIG. 1) for the use in fuelinjectors, but can be used in punching holes in any material. Holes inan orifice disc range in size from about 0.100 mm to about 0.300 mm ormore, but are unlikely to exceed 0.600 mm in multi-hole orifice discs.The thickness of the material 12 used in the manufacturing of orificediscs typically range from 0.076 mm to 0.203 mm. However, in someapplications, the thickness of the material 12 can be 0.254 mm or 0.300mm. The punch assembly 10 can be arranged to punch angled holes (e.g.,20 degrees and up to about 45 degrees) in the material 12. Themagnetostrictive device 14 will operate in these ranges and can beconfigured to extend its operating range by using a 2:1 or 3:1 hydraulicor mechanical amplifier.

FIG. 2 shows a pump assembly 10′ in accordance with another embodimentof the invention. In order to increase punch travel, the assembly 10′includes a pivoting mechanical lever 40 as a mechanical amplifierbetween portions 28 and 28′ of the punch. A second spring 32′ isprovided between portion 28′ of the punch and the punch holder/stripperplate 30. With reference to FIG. 2, α is the angular displacement of thelever 40 and, for any given α, the following relationship is defined:l ₁ /h ₁ =l ₂ /h ₂

The magnetization force, and therefore the amount of stretching of themagnetostrictive member 22, is determined primarily by the current incoil 26 and number of coil turns. The number of coil turns may becalculated or experimentally determined for a given configuration. Thecoil current should be maintained within a reasonable range that wouldavoid saturating the magnetostrictive material or dissipating excessivepower in the coil. In a preferred embodiment, the current can be variedby an external driver or determined from the operating voltage and coilresistance.

By using the magnetostrictive device 14 to drive an individual punch 28in the punch assembly 10, the benefits of high velocity and compactnesscan be realized in making orifice holes in an orifice disc. The highvelocity, (i.e., 3000 strokes per minute) makes a cleaner hole, resultsin better tool life, yields a more stable process in making orifice discwhich will yield orifice discs with less variance.

The term “magnetostriction” literally means magnetic contraction, but isgenerally understood to encompass the following similar effectsassociated with ferromagnetic materials: the Guillemin Effect, which isthe tendency of a bent ferromagnetic rod to straighten in a longitudinalmagnetic field; the Wiedemann Effect, which is the twisting of a rodcarrying an electric current when placed in a magnetic field; the JouleEffect, which is a gradual increasing of length of a ferromagnetic rodwhen subjected to a gradual increasing longitudinal magnetic field; andthe Villari Effect, which is a change of magnetic induction in thepresence of a longitudinal magnetic field (Inverse Joule Effect).

While the present invention is described primarily with reference toTerfenol-D as a preferred magnetostrictive material, it will beappreciated by those skilled in the art that other alloys having similarmagnetostrictive properties may be substituted and are included withinthe scope of the present invention. Furthermore, permanent magnets (notshown) can be employed to bias the Terfenol-D magnetic domains invarious coil combinations.

Control of the punch assembly 10, 10′ can be achieved, for example, withthe control strategy disclosed in U.S. Pat. No. 6,720,684, the contentsof which is hereby incorporated by reference in its entirety into thisspecification.

The foregoing preferred embodiments have been shown and described forthe purposes of illustrating the structural and functional principles ofthe present invention, as well as illustrating the methods of employingthe preferred embodiments and are subject to change without departingfrom such principles. Therefore, this invention includes allmodifications encompassed within the spirit of the following claims.

1. A punch assembly comprising: a die constructed and arranged tosupport material to be punched, and a magnetostrictive device includinga coil, a magnetostrictive member, and a punch operatively associatedwith the magnetostrictive member, the magnetostrictive member beingconstructed and arranged to lengthen when exposed to a magnetic fieldcreated by the coil, whereby, when the coil is energized and themagnetostrictive member lengthens, the punch moves through the materialand into the die, thereby creating a hole in the material.
 2. The punchassembly of claim 1, further comprising a plate associated with thepunch and the material to be punched, the plate having a bore therethrough, a portion of the punch being received for movement within thebore of the plate.
 3. The punch assembly of claim 2, further comprisinga spring between a surface of the punch and a surface of the plate, thespring being constructed arranged to prestress the magnetostrictivemember.
 4. The punch assembly of claim 1, in combination with thematerial to be punched, the material to be punched being an orifice discof a fuel injector.
 5. The punch assembly of claim 4, wherein the punchis constructed and arranged to punch holes in the orifice disc in arange generally between 0.100 mm and 0.600 mm.
 6. The punch assembly ofclaim 4, wherein the punch is constructed and arranged to punch holes inthe orifice disc in a range generally between 0.100 mm and 0.300 mm. 7.The punch assembly of claim 1, wherein the punch is constructed andarranged to punch holes in a range generally between 0.100 mm and 0.600mm.
 8. The punch assembly of claim 1, further comprising a mechanicalamplifier associated with the punch and constructed and arranged toincrease travel of the punch.
 9. The punch assembly of claim 1, whereinthe magnetostrictive member comprises Terfenol-D.
 10. A punch assemblycomprising: a punch constructed and arranged to punch a hole inmaterial, and magnetostrictive means, operatively associated with thepunch, for moving the punch from a first position to a second positionso as to punch a hole in the material, upon exposure of themagnetostrictive means to a magnetic field.
 11. The punch assembly ofclaim 10, in combination with the material, wherein the material is anorifice disc of a fuel injector.
 12. The punch assembly of claim 11,wherein the punch is constructed and arranged to punch holes in orificedisc in a range generally between 0.100 mm and 0.600 mm.
 13. The punchassembly of claim 10, wherein the magnetostrictive means includes amagnetostrictive member comprising Terfenol-D.
 14. The punch assembly ofclaim 10, further comprising a mechanical amplifier associated with thepunch and constructed and arranged to increase travel of the punch. 15.A method of punching a hole in material including: providing amagnetostrictive device including a coil, a magnetostrictive member, anda punch operatively associated with the magnetostrictive member, themagnetostrictive member being constructed and arranged to lengthen, whenexposed to a magnetic field created by the coil, thereby moving thepunch, associating material to be punched with the punch, and energizingthe coil to create a magnetic field and thus lengthen themagnetostrictive member so that the punch moves through the material,creating a hole in the material.
 16. The method of claim 15, wherein thestep of placing the material includes placing an orifice disc of a fuelinjector on a die.
 17. The method of claim 15, wherein themagnetostrictive member comprises Terfenol-D.
 18. The method of claim16, wherein the hole created in the orifice disc is in a size rangegenerally between 0.100 mm and 0.600 mm.
 19. The method of claim 15,further including: providing a mechanical amplifier and using themechanical amplifier to increase travel of the punch.
 20. The method ofclaim 15, further including prestressing the magnetostrictive memberprior to energizing the coil.